1. Field of the Invention
The invention relates to physical vapor deposition, and more particularly, to a method and apparatus for controlling a darkspace gap within a physical vapor deposition chamber.
2. Description of the Related Art
Sputtering is a physical vapor deposition (PVD) process in which high-energy ions impact and erode a solid target and deposit the target material on the surface of a substrate such as a silicon wafer. In semiconductor fabrication the sputtering process is usually accomplished within a semiconductor fabrication chamber also known as a PVD process chamber or a sputtering chamber.
A typical semiconductor fabrication chamber has a disc-shaped target of solid metal or other material supported by a backing plate that holds the target. Material sputtered from the edges of the target may contribute to a non-uniform deposition of the material on the surface of a substrate within the PVD chamber. To promote uniform deposition, the PVD chamber may have an annular concentric metallic ring often called a darkspace shield which circumferentially surrounds the disc-shaped target. The gap between the inner surface of the darkspace shield and the circumferential surface of the target is typically referred to as the darkspace gap.
In many applications, it is preferred that the darkspace gap be kept large enough to inhibit or prevent electrical arcing between the target and the darkspace shield which are often at different electrical potentials. On the other hand, it is often preferred that the darkspace gap be kept small enough to prevent PVD plasma ignition within the gap and also to reduce the amount of sputtered material entering the darkspace gap and depositing onto the circumferential surface of the target. Such depositions on the target edge may cause particle contamination on processed silicon wafers or other workpieces. To provide a suitable darkspace gap around the complete periphery of the target, proper alignment of the target and the darkspace shield is often needed. In prior sputtering chambers, the target and the darkspace shield are typically each aligned to the chamber body in which the target and darkspace shield are installed.